1. Field of the Invention
The present invention relates to a tire pressure monitoring device that monitors the pneumatic pressure of a plurality of tires of a vehicle.
2. Description of the Related Art
A related tire pressure monitoring device is disclosed in Japanese Unexamined Patent Application Publication No. 9-210827 (Patent Document 1). In the tire pressure monitoring device disclosed in Patent Document 1, as shown in FIG. 15, pneumatic pressure monitoring units A14 are individually installed for respective tires A12, an RF receiver A18 receives pneumatic pressure data, transmitted by radio from each pneumatic pressure monitor unit A14, by one common antenna A16, and a processor A20 distinguishes between characteristic identification codes (ID) of the respective tires to determine from which pneumatic pressure monitoring unit of the tire that the data, such as the pneumatic pressure data, is received.
However, in the tire pressure monitoring device disclosed in Patent Document 1, since each ID is previously registered, such as at the time of shipment of a vehicle, when, for example, tires mounted on the vehicle are replaced with spare tires, the positions at which the respective tires that are previously registered are mounted to the vehicle change. In such a case, it is necessary to register each ID again and to match the position of each tire on the vehicle with its ID. Therefore, it is necessary to register the IDs at a dealer each time the tires are replaced, which is inconvenient to perform.
To overcome this problem, Japanese Unexamined Patent Application Publication No. 2003-226121 (Patent Document 2) discloses a technique of determining from which pneumatic pressure monitoring unit of the tire that the data, such as the pneumatic pressure data, is transmitted without requiring the ID.
In a tire pressure monitoring device disclosed in Patent Document 2, as shown in FIG. 16, a right front wheel speed sensor B6, a left front wheel speed sensor B7, a right rear wheel speed sensor B8, and a left rear wheel speed sensor B9 are provided near a right front wheel tire B1, a left front wheel tire B2, a right rear wheel tire B3, and a left rear wheel tire B4, respectively, to determine the rotational speeds of the respective wheels and transmit each item of rotational speed data to an ABS control unit B11. In addition, pneumatic pressure monitoring units B10 provided at the respective tires transmit the centrifugal forces and the pneumatic pressures of the respective tires by radio to a tire pressure warning control unit B13. The fact that the size of the swing radius of each tire is different when the vehicle turns and travels is used to determine each axle speed based on centrifugal force information of each tire when the vehicle is turning and traveling. Then, this data and a detection result of each wheel speed sensor are compared to determine the position of each tire.
However, in the tire pressure monitoring device disclosed in Patent Document 2, since the centrifugal force information of each tire is the same when the vehicle is traveling in a straight line or when the vehicle is stopped, the position of each tire cannot be specified. When a signal is received from the pneumatic pressure monitoring unit of each tire, it cannot be determined for which tire the pneumatic pressure data is.
In addition, in the tire pressure monitoring device disclosed in Patent Document 2, it is necessary to provide individual wheel speed sensors near the respective tires and to perform wire routing from the wheel speed sensors to the control unit. Therefore, the number of parts and mounting costs are increased.